The present invention relates to rotors for use in blood pumps and to blood pumps having such rotors.
Implantable blood pumps are employed as ventricular assist devices to aid the functioning of a diseased heart in a human patient or non-human animal subject. When a blood pump is employed as a left ventricular assist device or “LVAD,” an inlet of the pump communicates with the left ventricle of the patient's heart, whereas the outlet of the pump communicates with the aorta downstream of the aortic valve. Thus, the pump acts in parallel with the patient's left ventricle to impel blood from the ventricle into the aorta. A pump used as an LVAD in a typical human subject should be capable of providing substantial blood flow as, for example, a few liters per minute or more, against a pressure head corresponding to the blood pressure of the subject. For example, in one typical operating condition, an LVAD may pump 5 liters of blood per minute at 75 mmHg pressure head, i.e., a pressure at the outlet of the pump 75 mmHg higher than the pressure at the inlet.
Other blood pumps are applied as right ventricular assist devices. In this application, the inlet of the pump is connected to the right ventricle of the subject's heart, whereas the outlet of the pump is connected to a pulmonary artery. Dual pumps can be used to provide both left and right ventricular assistance, or even as complete artificial hearts.
Implantable blood pumps should be compact so as to facilitate mounting the pump within the patient's body. They should also provide high reliability in prolonged use within a patient, most typically years, or even decades of service. An implantable blood pump also should be efficient so as to minimize the power required to operate the pump. This is particularly significant where, as in most applications, the pump is powered by a portable battery or other portable power source carried on or in the patient's body. Moreover, the pump should be designed to minimize damage to the patient's blood. It should limit the amount of blood subjected to relatively high sheer stresses as, for example, 150 Pa or more, so as to minimize the damage to components of the blood.
One particularly desirable form of blood pump is disclosed in U.S. Pat. Nos. 7,699,508; 7,972,122; 8,007,254; and 8,419,609, all assigned to the present assignee. The disclosure of the foregoing patents is incorporated by reference herein. This type of blood pump is commonly referred to as a wide-blade axial flow blood pump. The pump includes a housing having a bore and a rotor disposed within the bore. The rotor has a hub extending along an axis and blades projecting outwardly away from the hub. The blades are spaced apart from one another around the axis so that the blades cooperatively define channels extending between adjacent blades. The channels are generally helical and extend along the axis while also wrapping partially around the axis. The outer ends of the blades have tip surfaces facing in the outward direction, away from the axis. These tip surfaces have substantial area. The tip surfaces include hydrodynamic bearing surfaces. Typically, the rotor is magnetic and includes two or more magnetic poles. Electrical coils are arrayed around the housing. These coils are energized by an electrical power source so as to provide a rotating magnetic field, which spins the rotor. As the rotor spins, it impels blood axially in the housing, in a downstream direction along the axis. The hydrodynamic bearing surfaces support the rotor on a film of blood disposed between the bearing surfaces and the inner wall of the housing. Stated another way, the hydrodynamic bearings maintain the rotor coaxial with the bore and resist loads transverse to the axis of the rotor as, for example, loads imposed by gravity or gyroscopic forces that can be created when movement of the patient tilts the pump. Magnetic interaction between the rotor and the magnetic field applied by the coils resists axial movement of the rotor. In other variants, additional elements such as additional magnets or additional hydrodynamic bearings can be provided to resist axial movement of the rotor relative to the housing.
Preferred wide-blade axial flow pumps according to the aforementioned patents can be extraordinarily compact. For example, a pump suitable for use as a left ventricular assist device may have a rotor on the order of 0.379 inches (9.63 mm) in diameter and blades with an axial extent of about 0.5 inches (12.7 mm). The overall length of the rotor, including hubs projecting upstream and downstream from the blades is about 0.86 inches (21.8 mm). The housing has an inside diameter only slightly larger than the diameter of the rotor. The electrical coils, housing, and rotor may be contained within an outer shell about 0.7 inches (18 mm) in diameter and on the order of 1 inch (25 mm) long. In one arrangement, the outlet or downstream end of the housing is connected to a volute, which serves to connect the outlet end to an outflow cannula, whereas the inlet or upstream of the housing is inserted into the patient's left ventricle through a small hole in the heart wall. In still other arrangements, the entire pump may be positioned within the left ventricle, and the outlet end of the housing may be connected to an outflow cannula that projects through the aortic valve. See, U.S. Patent Application Publication No. 20090203957 A1, the disclosure of which is incorporated herein.
The wide-blade axial flow blood pumps according to the aforementioned patents and publication operate without wear. In operation, the rotor—the only moving part of the pump—is suspended by the hydrodynamic bearings and magnetic fields and does not touch the housing. Such a pump has theoretically infinite life. Moreover, preferred pumps according to the aforementioned patents can operate for many years without thrombus formation.
Despite the significant progress in the art, still further improvements would be desirable. In particular, it would be desirable to provide greater efficiency, improved pump performance, and reduced shear on the blood while still maintaining the advantages of the wide-blade axial flow blood pump. Such improvement poses a formidable engineering challenge. In a wide-blade axial flow pump of this type, the tip surfaces of the rotor blades must provide sufficient area for effective hydrodynamic bearings. The blades of the rotor must also have the volume needed to contain enough magnetic material to provide magnetic poles with sufficient strength on the rotor. These constraints have limited the possible improvements in design of the rotor heretofore.